Addison's disease is a rare, chronic endocrine disorder that occurs when the adrenal glands do not produce enough of the hormones cortisol and aldosterone. As a result, blood levels of cortisol and aldosterone are typically lower than normal for someone without Addison's disease.
The most common blood test used to diagnose Addison's disease is the ACTH stimulation test. This test measures the response of cortisol and aldosterone to a synthetic form of ACTH, a hormone that stimulates the adrenal glands to produce cortisol and aldosterone.
In this test, a blood sample is taken before and after administration of the ACTH hormone to measure the levels of cortisol and aldosterone. Typically, in someone with Addison's disease, the levels of both hormones will be low before administration of the ACTH hormone and will not rise significantly after administration.
In general, a healthy person's cortisol level should be greater than 20 mcg/dL before the ACTH injection and should rise to over 30 mcg/dL after the injection. Aldosterone levels should be greater than 7 ng/dL before the injection and should rise to over 10 ng/dL after the injection.
If the results of the ACTH stimulation test show that the levels of cortisol and/or aldosterone are lower than the normal range, it could indicate Addison's disease. Further tests, such as a CT scan or MRI of the adrenal glands, may be necessary to confirm the diagnosis.